U.S. patent application Ser. No. 953,637, filed Oct. 23, 1978, and U.S. patent application Ser. No. 953,788 filed Oct. 12, 1978, relate to similar subject matter by the same applicant herein.
The present invention relates to a new and improved method of, and apparatus for, monitoring faults at electrical lines, wherein a trigger or trip signal is formed for each line phase composed of line current and line voltage as a function of the distance between the measuring location and the fault location. Furthermore, the present invention relates to apparatus for the performance of such method employing measuring value-transducers or transformers for line current and line voltage for each phase to be monitored of the network system as well as a fault distance-measuring device for the distance-selective generation of a trigger or trip signal.
One proposal for distance-selective fault monitoring of the aforementioned character is known, for instance, from Brown Boveri Mitteilungen, 1966, Volume 53, pages 784-790, wherein electronic means detect relative phase angles between different voltage signals, partially derived by means of line simulation impedances, and such voltage signals are subjected to threshold monitoring. The trigger or trip curve--e.g. in the imaginary input impedance plane--in this case is circular. On the other hand, a relay trigger or trip curve which can be freely configured, according to the momentary protection requirements, cannot be readily realized, especially where there is used only one measuring system for each monitored phase.